Lecture 1: Orientation; species ranges and limiting factors
All “columbines” have extensions that go back behind the flower called nectar spurs and the
plant secretes sugar water that piles up in the bottom of the spur. The blue one (Aquilegia
caerulea) is adapted for pollination by extremely long tongued hock-moths (day-flying moths
that come to these flowers and push their tongues all the way down). The red one (Aquilegia
elegantula) is adapted for pollination by hummingbirds which also have a very long tongue but
not as long and flexible as a hock-moth. The spurs of the red one are considerably stiffer. The
red one and blue one are relatives.
Definition of Ecology => is the science of the distribution and abundance of organisms.
The most fundamental aspect of ecology is that everything is patchy. Organisms are not spread
neither evenly nor randomly across the world.
Eastern Washington State is more short grassland and semi-dessert in the low lands but the
mountains catch enough rain that they are green and forested (patchiness at regional scale).
There are also microhabitat variations.
The Carrizo plains _ a semi-desert in California _ if there’s been a lot of snow in the winter, these
deserts are moist enough in the spring that there’s a big bloom of annual plants. All the plants
then flower in different colors.
Abiotic factors are physical and chemical attributes of nature that have an important influence
Biotic factors are biological factors or living organisms that affect each other.
Abiotic (physical/chemical) factors:
Resources & Conditions
• Resources are exhaustible: nutrients,
• Conditions are not exhaustible:
temperature, pH, salinity, etc.
• Conditions vary across space and time; We envision
gradients of conditions
• Organisms perform best at certain levels, i.e., at
certain portions of a gradient
Difference between resources and conditions: resources are actual substances that organisms
need to carry out their metabolism/life processes. Resources are exhaustible. Plants need
Nitrogen in various chemical forms to grow. They need that as fertilizer. Same with water. These
resources will eventually be all used up and gone.
Conditions are not exhaustible. Temperature is an extensive property that is not depletable. Resources and conditions vary from place to place. We can imagine arranging different places in
gradients from high to low levels of any particular factor.
Range of tolerance => the set of levels of a factor that determine an organism’s success along
Lethal zones are death zone where necessary conditions for 1) individual survival, 2) growth or
3) reproduction do not exist.
There is a death zone on Mt. Everest where O 2oncentration is 1/3 that of sea level.
What factors are most important?
(Generalizations of breathtaking audacity!)
• For terrestrial plants (ground):
Soil moisture (for typical plants that have a root system that goes
into the soil to get water)
Nutrients (N most important, then P, K)
Disturbance (esp. fire)
Herbivory, disease, pollinators, seed dispersers, mycorrhizal fungi
• For aquatic plants:
Add salinity, remove moisture & fire, P key
Environmental variation sets limits on where organisms can thrive and where they can’t thrive.
Soil qualities => availability of certain chemicals that plants need.
Disturbance can be human disturbance like farming or natural disturbance like fire.
Herbivory: interactions with other species. Plants get eaten by animals.
Plants catch diseases.
Plants interact with insects or other animals that can pollinate their flowers and disperse their
There are interactions between plants and fungi, much of which are rather cryptic and take
place underground or inside the tissues of the plant.
For aquatic plants, there is a big difference for plants growing in fresh water as opposed to salty
water or brackish water which would be in between.
The factors on the top of the list (e.g. temperature) tend to concern larger spatial scale whereas
the ones at the bottom of the list concern smaller scales.
What factors are most important?
(Generalizations of breathtaking audacity)
• For terrestrial animals:
Food and water
Habitat quality (cover, nesting sites)
• For aquatic animals:
Add salinity/osmotic pressure
• So, animals will tend to follow plants If animals have access to food and water they are able to persist in more difficult environments.
Habitat quality is important in the sense that animals need particular physical features for
nesting, for taking cover from predators, some animals have to burrow in the soil to escape
Most chemical reactions depend very much on temperature.
Gradients at the global level: temperature, rainfall, Seasonality
• Temperature mostly a function of latitude
• Higher latitudes colder; seasonality a function of temperature (summer-winter)
• Lower latitudes warmer; seasonality a function of rainfall (dry season-wet season)
• Rainfall mostly depends on atmospheric circulation, offshore ocean currents, rain shadows
• These factors determine biomes.
It’s warm near the equator and cold near the poles.
Seasonal patterns have to do with the fact that the Earth is tilted on its axis of rotation.
In regions like Toronto, 44 degrees we have hot summer when our part of the globe leans
toward the sun and we have a cold winter when we lean away from the sun.
Seasonality in high latitudes is manifested as the alternation of a hot season-cold season in the
Seasonality in lower latitudes in tropical and sub-tropical regions is expressed in terms of
alternating wet and dry se